There exists an increasing demand for these products due to the fact that modern automobile engines operate under more severe conditions, requiring a lubricating oil which is formulated based on a base oil having the above specifications. The API Group II base oils are also valuable for Industrial Lubricants, because of their improved inhibited oxidation stability.
A process to prepare API Group II base oils is described in WO-A-0073402 This patent publication describes the preparation of such a base oil from a petroleum fraction boiling in the lubricating oil range by first removing part of the aromatic compounds from a by means of solvent extraction, subsequently dewaxing the solvent extracted product and hydrotreating the dewaxed oil using a suitable sulphided hydrotreating catalyst. The effluent of the hydrotreating step is subsequently separated into a gaseous fraction and a liquid fraction; wherein the liquid fraction has a sulphur content of between 50 and 1000 ppmw and a nitrogen content of less than 50 ppmw. This liquid fraction is subjected to a second hydrotreating step using a catalyst comprising a noble metal component supported on an amorphous refractory oxide carrier.
The above process is not preferred because it involves many process steps to obtain the desired base oil.
U.S. Pat. No. 3,673,078 discloses a counter-current contacting of a solvent refined base oil using a platinum on alumina catalyst. The temperature in the bottom catalyst bed was 343° C. and the difference between the temperature in the top and the bottom catalyst bed was about 14° C.
Although the disclosed processes may be used to prepare low sulphur and low polar compounds containing base oils there is still room for improvement.